Metal-catalyzed asymmetric synthesis of P-stereogenic Phosphines

This account summarizes our attempts to develop metalcatalyzed asymmetric syntheses of P-stereogenic phosphines. While such phosphines undergo pyramidal inversion slowly at room temperature, inversion is rapid in metal-phosphido complexes (M-PR2). These observations were the basis for catalytic, dynamic kinetic resolution processes in which racemic secondary phosphines [PR(R')H] were converted into enantioenriched tertiary phosphines [PR(R')(R")] by platinurn-catalyzed asymmetric hydrophosphination of acrylonitrile or related Michael acceptors, by palladium-catalyzed asymmetric phosphination of aryl iodides using secondary phosphines or phosphine-boranes, and by platinurncatalyzed asymmetric alkylation of secondary phosphines. The key intermediates were diastereomeric phosphido complexes with chiral ancillary ligands (L-n*-M-PRR'). Their relative rates of P-inversion and phosphorus-carbon bond formation controlled the enantioselectivity of product formation, whether the phosphorus-carbon bonds were formed by reductive elimination (for Pd), or by the reaction of a platinum-phosphido complex with an electrophile (an alkene in hydrophosphination, or a benzyl bromide in alkylation). The results of mechanistic studies and their use in the design of improved catalytic reactions are described. 1 Introduction 2 Phosphorus Inversion 3 Platinum-Catalyzed Asymmetric Hydrophosphination 4 Palladium-Catalyzed Asymmetric Phosphination 4.1 Secondary Phosphines 4.2 Secondary Phosphine-Boranes 5 Platinum-Catalyzed Asymmetric Alkylation of Secondary Phosphines 6 Conclusion.